xzax

I'm a fairly new lexus owner (under 2 years). I have had pretty much zero issues with this car until recently. My brakes were feeling spongy and depressing much more easily and further than before. The car still stopped, there were no odd noises or indicator lights. I did note that when coming to a stop sometimes the pedal would travel near the floor and the trac control light would come on until I resumed forward.

I don't have a good area for working on cars, so I did a little research and thought I'd just go through the issue one thing at a time. I took it to a local mechanic who agreed to flush the fluid and change out brake pads for me. They wanted to change the front rotors, so I let them do that. They said they had micro-fractures. I think they just fed me bs.

After they were done they said they tested it and it does stop but...
a) the pedal is still too mushy
b) it doesn't stop as well as it should
c) when in drive I can depress the pedal to the floor and this causes the trac control light to come on, this does not happen in park
d) the brakes squeak now, after over a week of driving
e) there is steering wheel feedback when using the brakes
f) the brakes slightly stick when releasing

The conversation I had with the mechanics about this led me to not trust them further as they wanted me to believe this was normal AND never offered what else could be wrong (ie master cylinder, etc).

So after wasting my money I was basically in worse shape than before and had no real confidence in what was done or not done properly. I could just kick myself in the backside ( I try but I just keep falling over ).

I can't find a service manual for this car (Haynes, etc). I'm wondering if I can get one from the dealer or if a Toyota Avalon manual might work? I want this because I've seen a few discrepancies in the brake bleeding protocols I've seen for Lexus. I saw some mention of a "rear" brake pump and the need to have power on when doing the rear. I saw one guy talking about pumping like 40 times with power off and then 20 with it turned on... admittedly he was changing the whole master cylinder.

I read a couple really good threads on this forum but I think they were for the LS and IS models so I don't know if they apply. In these threads it was suggested this issue isn't usually the master cylinder. It can be caliper pistons or not bleeding correctly. Maybe the brake booster or even reservoir cap. Even the vaccum check valve...

I've almost become dizzy with the possibilities without a proper manual. I may end up taking it to the dealer but honestly I haven't met a mechanic in this state that I trust so before I do that I want to understand the components in the system and have checked as much as I can. It just makes things better when talking to them.

What I've done:
1. Checked for leaks. The master reservoir has never gone low or seemed to leak any fluid. No fluid can be seen anywhere. Maybe the master is leaking internally but I'm not ready to throw 600 dollars at one to find out yet.
2. Checked rear rotors/pads, bled rear brakes (passenger then driver side). Rotors bit worn and crusty around outside edge.
3. Checked front pads/rotors (verified new rotors are OEM), had rotors turned.
4. Bled front brakes (passenger then driver), start car pump up brakes to seat.
Bleeding was done using vacuum method with mityvac.

Squeaking gone, steering feedback gone, gripping on release gone (so all the problems the mechanics introduced and I paid for are fixed).
Brakes are very mushy.
Brakes not stopping even as well as after took to mechanic, but they do stop.
When in drive can push brake pedal to floor and trac control light comes on, no other lights.

So of course it seems like a master cylinder but before I tackle that I'd like this forum's advise.

Do you know a service manual for this car?
Is there a special process for bleeding the brakes on this vehicle (ex rear brake pump)?
Components I haven't considered or know about?
Advise/Resources on trouble-shooting this issue?

I believe I can replace the master on this car myself but I am wary to do that without a good deal of knowledge regarding this process (model specific) and making sure I get everything purged and reset properly...otherwise it's just a trip to the dealer anyway.

Thanks for any input.

Cheers,

Doug

aachowhan

What color is the fluid? Did you do a flush?

Sometimes certain brake pad and rotor combos just don't work well together. Any idea what pads and rotors are on your car?

GrandSedanFan

iTrader: (1)

Yikes. Definitely warrants a trip to the dealer. We have Electronic Controlled Brakes (ECB), a brake by wire system, so a soft pedal is doubly troubling. Under normal operation, the pedal feedback should be entirely simulated.

https://pressroom.lexus.com/lexus-sa...ature-summary/

While there is a physical connection between the brake pedal and master cylinder, that connection is not active unless the ECB system fails. Based on what you've provided, your issue could be just as much a software/electronic issue as a physical/maintenance issue.

Good luck and keep us posted.


EDIT: There was some question below as to whether the 4GS has ECB. My understanding, based on the following Lexus published materials, is that it does.

GregCanada

It sounds like, perhaps the soft/flex lines are failing?

xzax

Hello and thank you for responding.

The color of the brake fluid was only a little darker than stock. The mechanics said they flushed it and the fluid was different (clean) after they finished. After I had the new rotors off and turned I bled the brakes front and back and made sure I purged all the old fluid and put in fresh.

The mechanics also changed the rotors and pads. Since I had a bit of an argument (5 dudes in small office squared off against me but ended up with head's hanging down) I found they are not terribly forth coming with information, plus I just don't trust them. I did source the rotors the mechanics put on when I took them back off to have them turned (when people say new rotors don't need turned, I think they are just repeating marketing garbage that has filtered down as proper practice... the difference is night and day) and found the new rotors were OEM. The pads I don't know. I could find out and I may replace them, but I'll do some more digging before that.

Thanks again for the help. What I really need is a service manual for this car.

Doug

xzax

Thank you, that is good information I will add to my already unorganized and confused mind

After consulting with the best mechanic I know and comparing to other brake issues I've read about here I think I may have not bled the brakes properly or perhaps I did but I made a mistake.

I think when bleeding I may have let the reservoir go below min and started over but I didn't bleed at the master and I don't think the mityvac is up to the task of pulling air from "difficult" areas.

I'm going to bleed the brakes again using the "pressurized" method and finish with bleeding the master. After that I'm going to check the caliper pistons aren't stuck and I'll be taking the suggestion from below and checking/replacing lines that may be flexing/bulging under pressure.

I'm very much hoping it still has air in the lines and if not I'll keep trying to pin it down by process of elimination. If I can't get it to improve I'll end up at the dealer but I'm not ready to give in yet as I haven't properly eliminated all the easy stuff.

Thanks so much for your suggestions and provided information. Any clues about a service manual would be appreciated.

Regards,

Doug

xzax

I'll definitely have another look at all the hoses. I've kind of posted what I think I'll be doing. The hoses were on my mind this whole time but I didn't see anything obvious so I hadn't "gone there" yet. Thanks for the help it's super appreciated.

Doug

Knucklebus

The flex lines should show visible bulges when you press the brake pedal forcefully. The outer covering would look cracked and splitting if it were really bad. You should have at least 4 flex lines. One at each wheel.

You might try turning off the traction control to see if it feels any different. I learned that the ABS works even when the traction control is turned off when I ran mine on the lift. You cannot stop the wheels in drive if they aren't touching the ground.

Find a safe spot and try a panic stop from 15-20MPH to see how it responds.

Also, see if you have any codes stored that aren't popping the check engine light.

er34

Your link literally says:

A component of VDIM is the Electronically Controlled Brakes (ECB), a "brake-by-wire" system (except in IS 250, IS 350, IS F and GS 350).

Yri

Not to mention it is an older article from 2010. At that time, it appears the only GS with ECB was the GS460. According to the more modern product information brochures, all 4th gen GS' have a conventional brake system.

GrandSedanFan

iTrader: (1)

I was citing my source for the definition of ECB. The link was from 2010 and referred to the 3GS. My understanding is that the 4GS has ECB.

Page 2 of the below PDFs - 2013 GS350 Knowledge Center, 2015 GS350 Knowledge Center, both published by Lexus.
"Four-wheel power-assisted discs, with four-sensor, fourchannel Anti-lock Braking System (ABS), Electronic Brakeforce Distribution (EBD) and Brake Assist. Electronic Controlled Braking (ECB). 13.1-in front, 12.2-in rear ventilated discs (GS 350). 14.0-in front/rear ventilated (RWD F-Sport)." Emphasis mine.
https://lexus2.custhelp.com/ci/fatta...B%20031914.pdf
https://lexus2.custhelp.com/ci/fatta...015+GS+REB.pdf

2019 GS350 Press Kit, published by Lexus.
"Vehicle Dynamics Integrated Management (VDIM) system integrates and manages ECB, ABS, BA, EBD, VSC and Electric Power Steering (EPS)" Emphasis mine.
https://pressroom.lexus.com/2019-lexus-gs-press-kit/

2013 GS450h Press Release, published by Lexus.
"The GS 450h’s Electronically Controlled Braking (ECB) system characteristics have been modified to provide greater responsiveness from the first touch of the pedal."
https://pressroom.lexus.com/new-2013...rt-motor-show/

Can you share your sources? I was certain that our consistent pedal feel was due to the ECB, and the above referenced materials published by Lexus appear to indicate so as well.

xzax

Thanks for the helpful extra information. I'm waiting for the service manual and I ordered a new scanner to hopefully help me do exactly what you are suggesting. I should be able to get back into this project this weekend armed with better information about the system, trouble-shooting and repair operations and the ability to use a computer to help bleed the ABS, look at codes and get bi-directional information. I think I'm going to try to document and post what I find as it seems this forum is full of cool people and we could all use more accurate information. I may even make the service manual available if copyright doesn't stop me.

Also I had tried brakes w/o trac control, they act the same. I also tried slamming on the brakes from speed both with and wo trac. Same issues, car stops, really doesn't seem much difference between the two. I can get it to lock the tires but it's so mushy it feels very unsafe. I'll test that more carefully once I get back into things this weekend.

Thanks Again,

Doug

xzax

No worries mate. I looked at your reference material the other day. It did concern me that this was a more complex issue than I had hoped. With that in mind I managed to find a service manual on ebay that should be for this car (fingers crossed). I also grabbed a new scan tool (D7) to help get a look at what the computer says and I believe it will help with properly bleeding the brakes "by the book".

I have looked at quite a few videos of folks working on lexus braking systems, specifically master cylinders. My guess is many of the 2000 models do have a very complex master cylinder/abs where there is a canister to hold pressure and a small engine and pump attached to charge it. This is clearly electrically controlled as you were concerned about. I had a good look at my master last nite and it's just a basic unit. I'm not sure either way but that's why I ordered the service manual.

I believe I'll document and post what I find and what fixes it. I may even try to make the manual available somehow as it seems we are a bit short on resources for this model.

Thanks so much for the amount of effort you put into reading and trying to help me safely approach this issue. I really appreciate it.

Doug

jgscott

iTrader: (1)

I would be looking for some kind of of Vacuum line, or pressure leak from the Booster or something air related like that.

A pin hole air pressure leak could cause that condition. I might not even be visible until you brake and it has pressure. If it was me.